The cost of providing detention facilities to cope with ever increasing numbers of individuals requiring detention, such as convicted criminals, defendants awaiting trial or suspects, has led many local and state government justice systems to alternative forms of sentencing and detention including house arrest with electronic monitoring. Conventional house arrest monitoring systems utilize a radio transmitter, with associated control electronics, that is affixed to the person under house arrest with a wrist or ankle band. The radio transmitter periodically transmits a one-way coded signal to a radio receiving apparatus at a base station. The radio receiving apparatus is connected to a telephone line to enable communication with a monitoring service. Electronic circuitry within the radio receiving apparatus provides either automatic answering or automatic periodic dialing to effect communication with the monitoring service, thereby enabling the monitoring service to determine the status of the monitored person under house arrest. The radio receiving apparatus supplies an alarm signal to the monitoring service system if the receiving apparatus fails to receive the coded signal from the radio transmitter, as failure to receive the coded signal is interpreted as indicating that the monitored person has moved outside the confines of the permitted house arrest area.
Conventional house arrest monitoring systems of the type described above are subject to a number of deficiencies. For example, the devices do not issue a warning to the wearer as to maximum range of communication, i.e., when the boundary of the house arrest area is approached. Thus, the wearer may inadvertently cross the boundary and violate the house arrest conditions or in some manner defeat the device by creating physical barriers to transmission. In addition, if the wearer intentionally violates the house arrest conditions, the devices do not provide a mechanism for identifying the wearer as a violator to other individuals. Thus, the violator can often conceal or remove the ankle band or wrist band containing the transmitter and avoid detection as a violator. While the violation is reported to the monitoring service, the violator has the opportunity of fleeing and/or blending in with the general public before a description of the violator can be widely circulated. Conventional systems also use unsophisticated narrow band radio devices of a type generally used to operate garage doors or control the door locks of automobiles. The narrow band devices are only permitted to operate at very low transmit power levels and frequently do not provide sufficient range to permit sufficient tracking or full coverage of a violator's home or permitted house arrest area. In addition, technically knowledgeable individuals can easily defeat conventional systems due to a lack of security measures within their systems.
In view of the above, it is an object of the invention to provide a monitoring system that overcomes the deficiencies of conventional house arrest monitoring systems.